Display device and display method

ABSTRACT

According to one embodiment, a display device includes an image projection unit. The image projection unit is configured to project a light flux toward one eye of a human viewer by using a projection plate to reflect the light flux. The light flux includes an image including a display object having a vanishing point. The projection plate is reflective and transmissive. The image projection unit is configured to dispose the vanishing point of the display object at a position different from a position of a vanishing point of a background image viewed by the human viewer through the projection plate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation application of International ApplicationPCT/JP2009/066750, filed on Sep. 28, 2009; the entire contents of whichare incorporated herein by reference.

FIELD

Embodiments of the invention described herein relate generally to adisplay device and a display method.

BACKGROUND

Head-up displays (HUDs) are being developed as automotive displaydevices to project display information such as destination navigationinformation and the like onto a windshield to allow simultaneous visualconfirmation of the external environment information and the displayinformation. Although the display of the HUD is viewed with both eyes inthe case of a normal HUD, binocular parallax occurs and the display isdifficult to view.

Conversely, a monocular HUD has been proposed in which the display isviewed with one eye (for example, refer to JP-A 2009-128565 (Kokai)).According to such a monocular HUD, a virtual image of the display objectcan be perceived at a spatial position that is matched to thebackground.

In such a monocular HUD, it is desirable for the depthward position atwhich the display object is disposed to match the perceived depthwardposition at which the display object is actually perceived with evenhigher precision.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A to FIG. 1C are schematic views showing operations of a displaydevice;

FIG. 2 is a schematic view showing the display device;

FIG. 3 is a schematic, view showing an image projection unit of thedisplay device;

FIG. 4 is a schematic view showing a coordinate system of the displaydevice;

FIG. 5A to FIG. 5D are schematic views showing a display object of thedisplay device;

FIG. 6 is a schematic view showing the configuration of the evaluationexperiment of the characteristics of the display device;

FIG. 7A to FIG. 7D are schematic views showing the conditions of theevaluation experiment of the display device;

FIG. 8A to FIG. 8D are schematic views showing the conditions of theevaluation experiment of the display device;

FIG. 9A to FIG. 9D are schematic views showing the conditions of theevaluation experiment of the display device;

FIG. 10A to FIG. 10D are graphs showing the experimental results of thedisplay device;

FIG. 11A to FIG. 11D are graphs showing the experimental results of thedisplay device;

FIG. 12A to FIG. 12D are graphs showing the experimental results of thedisplay device;

FIG. 13A to FIG. 13C are graphs showing the experimental results of thedisplay device;

FIG. 14A to FIG. 14D are schematic views showing operations of thedisplay device;

FIG. 15A and FIG. 15B are schematic views showing operations of thedisplay device;

FIG. 16 is a schematic view showing another display device;

FIG. 17 is a flowchart showing operations of the display device;

FIG. 18 is a schematic view showing the display device;

FIG. 19 is a schematic view showing the display device;

FIG. 20 is a schematic view showing the display device;

FIG. 21 is a schematic view showing the display device;

FIG. 22 is a schematic view showing the display device; and

FIG. 23 is a flowchart illustrating a display method.

DETAILED DESCRIPTION

According to one embodiment, a display device includes an imageprojection unit. The image projection unit is configured to project alight flux toward one eye of a human viewer by using a projection plateto reflect the light flux. The light flux includes an image including adisplay object having a vanishing point. The projection plate isreflective and transmissive. The image projection unit is configured todispose the vanishing point of the display object at a positiondifferent from a position of a vanishing point of a background imageviewed by the human viewer through the projection plate.

According to one embodiment, a display method is disclosed. The methodcan include projecting a light flux including an image including adisplay object toward one eye of a human viewer by using a projectionplate to reflect the light flux. The projection plate is reflective andtransmissive. The method can include disposing a vanishing point of thedisplay object at a position different from a position of a vanishingpoint of a background image viewed by the human viewer through theprojection plate during the projecting toward the one eye.

Embodiments of the invention will now be described in detail withreference to the drawings.

The drawings are schematic or conceptual; and the relationships betweenthe thicknesses and the widths of portions, the proportions of sizesamong portions, etc., are not necessarily the same as the actual valuesthereof. Further, the dimensions and the proportions may be illustrateddifferently among the drawings, even for identical portions.

In the specification and the drawings of the application, componentssimilar to those described in regard to a drawing thereinabove aremarked with like reference numerals, and a detailed description isomitted as appropriate.

First Embodiment

FIG. 1A to FIG. 1C are schematic views illustrating operations of adisplay device according to a first embodiment.

FIG. 2 is a schematic view illustrating the configuration of the displaydevice according to the first embodiment.

FIG. 3 is a schematic view illustrating the configuration of an imageprojection unit of the display device according to the first embodiment.

FIG. 4 is a schematic view illustrating a coordinate system of thedisplay device according to the first embodiment.

FIG. 5A to FIG. 5D are schematic views illustrating a display object ofthe display device according to the first embodiment.

First, the configuration of the display device 10 according to theembodiment will be described using FIG. 2 and FIG. 3. As shown in FIG.2, the display device 10 includes an image projection unit 115configured to project a light flux 112 that includes an image includinga display object 180 toward one eye 101 of a human viewer 100 by using areflective and transmissive projection plate 715 to reflect the lightflux 112.

The display object 180 is provided in the image that the display device10 presents to the human viewer 100 and is, for example, various displaycontent relating to the operation information of a vehicle 730 (a movingbody) in which the display device 10 is mounted such as an arrowindicating the travel direction, etc.

The projection plate 715 is, for example, a windshield 710 of thevehicle 730. The projection plate 715 may include a reflective andtransmissive optical layer that is formed on the windshield 710. Theprojection plate 715 may include a reflective and transmissive opticalcomponent that is additionally provided proximally to the windshield710. Thus, the projection plate 715 is the windshield unit of thevehicle 730 in which the display device 10 is mounted.

The image projection unit 115 projects the light flux 112 toward thehead 105 of the human viewer 100. In other words, the light flux 112emitted from the image projection unit 115 is reflected by a reflectivesurface 712 of the projection plate 715 and is incident on the one eye101 of the human viewer 100.

The human viewer 100 can simultaneously view the external environmentinformation of the vehicle 730 and the display object 180 of the imageincluded in the projected light flux 112.

As illustrated in FIG. 2, the display device 10 is provided, forexample, inside the vehicle 730, e.g., in an inner portion of adashboard 720 of the vehicle 730 as viewed by the human viewer 100 whois the operator.

The image projection unit 115 includes, for example, an image datageneration unit 130, an image formation unit 110, and a projection unit120.

The image data generation unit 130 generates an image signalcorresponding to the image including the display object and supplies theimage signal to the image formation unit 110.

Various optical switches such as, for example, liquid crystal displaydevices (LCDs), DMD (Digital Micromirror Devices), MEMS(Micro-electro-mechanical Systems), etc., may be used as the imageformation unit 110. The image formation unit 110 forms the image on thescreen of the image formation unit 110 based on the image signalsupplied from the image data generation unit 130.

On the other hand, the projection unit 120 may include, for example,various light sources, lenses, mirrors, and various optical elementsconfigured to control the divergence angle (the diffusion angle).

In the specific example, the projection unit 120 includes a first lens123, a second lens 125, and an aperture 124 (a divergence angle controlunit) provided between the first lens 123 and the second lens 125. Thesize of the opening of the aperture 124 may be variable. That is, avariable aperture may be used as the aperture 124.

More specifically, as shown in FIG. 3, the projection unit 120 includesa light source 121, a tapered light guide 122, the first lens 123, thesecond lens 125, the aperture 124, and a mirror 126.

The first lens 123 is disposed between the light source 121 and themirror 126; the second lens 125 is disposed between the first lens 123and the mirror 126; and the tapered light guide 122 is disposed betweenthe light source 121 and the first lens 123.

In the specific example, the image formation unit 110 (e.g., the LCD) isdisposed between the tapered light guide 122 and the first lens 123.

For example, the aperture 124 is mounted at a position that is adistance f1 from the first lens 123 and a distance f2 from the secondlens 125, where the distance f1 (the first focal distance) is the focaldistance of the first lens 123 and the distance f2 (the second focaldistance) is the focal distance of the second lens 125. In other words,the distance between the divergence angle control element and the firstlens 123 is the first focal distance; and the distance between thedivergence angle control element and the second lens 125 is the secondfocal distance.

The mirror 126 has, for example, a concave configuration. Thereby, themirror 126 can project an enlarged image of the light flux 112 to thehuman viewer 100. The light source 121 may include various light sourcessuch as LEDs (Light Emitting Diodes), high pressure mercury lamps,halogen lamps, lasers, etc.

By using an LED as the light source 121, the power consumption can bereduced; and the device can be lighter and smaller.

The divergence angle of the light emitted from the light source 121 iscontrolled to be within a certain range by the tapered light guide 122such that the light emitted from the light source 121 becomes the lightflux 112 that includes the image including the prescribed display object180 in the image formation unit 110. The divergence angle of the lightflux 112 is controlled to be a prescribed angle by passing through thefirst lens 123, the aperture 124, and the second lens.

In the specific example, a diffuser plate 127 is provided between thetapered light guide 122 and the image formation unit 110; and thereby,the light incident on the image formation unit 110 is more uniform.

As shown in FIG. 2, the light flux 112 reaches the one eye 101 of thehuman viewer 100 by being reflected by the projection plate 715 of thevehicle 730 after being reflected by the mirror 126.

At this time, for example, the light flux 112 is incident on the one eye101 of the human viewer 100, and the light flux 112 is not incident onthe other eye because a projection area 114 and a projection position114 a of the projection region of the light flux 112 are controlled byvarious optical elements included in the image projection unit 115. Forexample, the projection area 114 of the light flux 112 is controlled tobe about 65 mm (millimeters) in the lateral direction (the lateraldirection as viewed by the human viewer 100). For example, thelateral-direction width of the projection area 114 of the light flux 112at the position of the human viewer 100 as viewed by the human viewer100 is not more than 70 mm.

An aspherical Fresnel lens (not shown) may be provided on the emergingside of the mirror 126 (the side opposite to the light source). By suchan aspherical Fresnel lens, for example, the configuration of the imageincluded in the light flux 112 can be aligned by controlling theconfiguration of the light flux 112 to match the configuration of thewindshield 710.

The mirror 126 may be movable; and, for example, the light flux 112 canbe projected appropriately toward the one eye 101 by manually orautomatically adjusting the position and/or the angle of the mirror 126manually or automatically to match the position and/or the movement ofthe head 105 of the human viewer 100.

Other than the specific examples recited above, various modifications tothe image projection unit 115 are possible.

The human viewer 100 perceives an image 181 of the display object 180formed at the position of a virtual image formation position 181 a viathe projection plate 715. Thus, the display device 10 can be used as aHUD.

The display object 180 has a target, position that relates to the depthdirection as viewed by the human viewer 100. The target position of thedisplay object 180 will now be described.

Here, as viewed by the human viewer 100 as shown in FIG. 4, the depthdirection is taken as a Z-axis direction; the lateral direction (ahorizontal direction Ha) is taken as an X-axis direction; and thevertical direction (a perpendicular direction Va.) is taken as a Y-axisdirection. The direction away from the human viewer 100 is taken as thepositive direction of the Z-axis; the direction to the right of thehuman viewer 100 is taken as the positive direction of the X-axis; andthe direction upward from the human viewer 100 is taken as the positivedirection of the Y-axis.

The human viewer 100 views the display object 180 of the image of thelight flux 112 reflected at the reflective surface 712 of the projectionplate 715. At this time, in the case where the display object 180 is anarrow illustrating, for example, a route, the image 181 of the arrow ofthe display object 180 is disposed to overlap the position of a branchpoint 753 c of a road 753 of a background image 740 d. In other words,the depth-direction position of the branch point 753 c of the backgroundimage 740 d as viewed by the human viewer 100 is a target position PTwhere the display object 180 is to be disposed.

Thus, the display object 180 is disposed at the target position PT inthe visual space of the human viewer 100 to correspond to the desiredposition in real space (the space having the X1-axis, the Y1-axis, andthe Z1-axis). In other words, when displaying the display object 180 tocorrespond to any object (mountains, rivers, various buildings anddisplay objects, roads, branch points, etc.) existing in real space, thedisplay object 180 is disposed at the target position PT which is theposition of the object as viewed by the human viewer 100. Hereinbelow,the case is described where an arrow illustrating the route is used asthe display object 180.

Herein, the X-axis, the Y-axis, and the Z-axis of the position of thehuman viewer 100 in real space are parallel to the X2-axis, the Y2-axis,and the Z2-axis of the position of the background in real space,respectively. On the other hand, the X1-axis, the Y1-axis, and theZ1-axis of the reflective surface 712 may not be parallel to the X-axis,the Y-axis, and the Z-axis, respectively. In other words, as illustratedin FIG. 2, the reflective surface 712 of the projection plate 715 whichis the windshield 710 of the vehicle 730 is tilted (rotated around theX1-axis) as viewed by the human viewer 100. For easier viewing of thedrawing in FIG. 4, the X1-axis, the Y1-axis, and the Z1-axis are takento be parallel to the X-axis, the Y-axis, and the Z-axis, respectively.

Herein, the position of the one eye 101 of the human viewer 100 is takenas a reference point P0. The reference point P0 is different from thetarget position PT in the directions of each of the X-axis, the Y-axis,and the Z-axis in real space. In practice, because of the circumstancesin which the display device 10 is mounted and used in the vehicle 730,the differences in the vertical direction (the Y-axis direction) and thelateral direction (the X-axis direction) are small; and the differencein the depth direction (the Z-axis direction) is large. Therefore, thedepth direction (the Z-axis direction) distance between the targetposition PT and the position of the one eye 101 of the human viewer 100(the reference point P0) in particular is taken as a depthward setdistance Ld.

The display object 180 is disposed at, for example, the position of thebranch point 753 c as the target position PT. It is not always necessaryfor the target position PT to be set at the branch point 753 c; and thetarget position PT may be set at any position. For example, the displayobject 180 may be disposed at a frontward position (the target positionPT) at a prescribed distance as viewed by the human viewer 100 even inthe case where an arrow heading straight is used as the display object180. The prescribed distance recited above is set based on the movementspeed of the vehicle 730, the circumstances of the frontward road, etc.

A specific example of the disposition of the display object 180 will nowbe described.

FIGS. 5A and 5B illustrate the case where the display object 180 isdisplayed to correspond to the road 753 (the ground surface) of thebackground image 740 d; and FIGS. 5C and 5D illustrate the case wherethe display object 180 is displayed to correspond to a ceiling 754 (thesky) of the background image 740 d.

As shown in FIG. 5B, in the case where the position of the displayobject 180 of the reflective surface 712 is positioned lower than theone eye 101 of the human viewer 100 as viewed from the one eye 101 ofthe human viewer 100, the human viewer 100 views the display object 180as being superimposed on an object of the background image 740 d that islower than the line of sight. For example, the road 753 is used as theobject of the background image 740 d that is lower than the line ofsight.

In such a case, as shown in FIG. 5A, the display object 180 is displayedto correspond to the road 753 of the background image 740 d.

As shown in FIG. 5D, the human viewer 100 views the display object 180as being superimposed on an object of the background image 740 d that ishigher than the line of sight in the case where the position of thedisplay object 180 of the reflective surface 712 is positioned higherthan the one eye 101 of the human viewer 100 as viewed from the one eye101 of the human viewer 100. For example, the ceiling 754 is used as theobject of the background image 740 d that is higher than the line ofsight.

In such a case, as shown in FIG. 5C, the display object 180 is displayedto correspond to the ceiling 754 of the background image 740 d.

Three-dimensionally overlapping roads such as elevated roads and thelike, roads of tunnels and the like, and illumination, power lines, andthe like that are mounted overhead in the sky may be used as such anobject that is higher than the line of sight. In such a case, forexample, the reflective surface 712 is disposed on the roof side of thevehicle 730; and the display object 180 is viewed by the human viewer100 as being higher than the Z-axis direction.

Operations of the display device 10 according to the embodiment will nowbe described for the case where the display object 180 is displayed tocorrespond to the road 753 (the ground surface) of the background image740 d.

FIG. 1A schematically illustrates the image 181 of the display object180 and the background image 740 d of the external environment of thevehicle 730 that are perceived by the human viewer 100. FIG. 1Billustrates the image 181 of the display object 180 of a screen 110 d ofthe image formation unit 110 of the image projection unit 115. FIG. 1Cillustrates the background image 740 d of the external environment ofthe vehicle 730 that is perceived by the human viewer 100.

As shown in FIG. 1B, the display object 180 is formed in the screen 110d of the image formation unit 110 (e.g., the LCD). The display object180 has an arrow configuration.

The display object 180 has a vanishing point VP1 (a first vanishingpoint VP1).

In other words, the display object 180 has a configuration including thevanishing point VP1 that causes a perception of depth; and, for example,the extension lines of two sides 183 a and 183 b of the shaft portion ofthe arrow intersect at the vanishing point VP1. In other words, thedisplay object 180 has a configuration that includes a first side (theside 183 a) and a second side (the side 183 b); and the extension lineof the first side and the extension line of the second side intersect atthe vanishing point VP1 of the display object 180.

In the case where the display object 180 is disposed lower than thehuman viewer 100 as viewed by the human viewer 100 (e.g., the case ofthe configuration illustrated in FIGS. 5A and 5B), the vanishing pointVP1 is disposed higher than the position of the display object 180.

On the other hand, in the case where the display object 180 is disposedhigher than the human viewer 100 as viewed by the human viewer 100(e.g., the case of the configuration illustrated in FIGS. 5C and 5D),the vanishing point VP1 is disposed lower than the position of thedisplay object 180.

The human viewer 100 gets a sense of depth of the display object 180 asviewed by the human viewer 100 based on the positional relationshipbetween the vanishing point VP1 and the display object 180. Thus, it iseasier for the human viewer 100 to infer the depthward position of thedisplay object 180 by the display object 180 having the vanishing pointVP1.

For example, when the display object 180 is disposed at a position lowerthan a position of a center of the reflective surface 712 of theprojection plate 715 as viewed by the human viewer 100, the vanishingpoint VP1 of the display object 180 is disposed at a position higherthan a position of the vanishing point VP2 of the background image 740 das viewed by the human viewer 100.

On the other hand, as shown in FIG. 1C, the background image 740 d ofthe external environment of the vehicle 730 has a vanishing point VP2(the second vanishing point VP2). In the specific example, the road 753extending straight frontward as viewed by the human viewer 100 exists;and the extension lines of boundaries 753 a and 753 b on the two sidesof the road 753 substantially intersect (become a point) at thevanishing point VP2. Thus, the human viewer 100 gets a sense of depth ofthe background image 740 d because the background image 740 d has thevanishing point VP2.

For example, when the display object 180 is disposed at a positionhigher than a position of a center of the reflective surface 712 of theprojection plate 715 as viewed by the human viewer 100, the vanishingpoint VP1 of the display object 180 is disposed at a position lower thana position of the vanishing point VP2 of the background image 740 d asviewed by the human viewer 100.

In the display device 10 according to the embodiment as shown in FIG.1A, the vanishing point VP1 of the display object 180 is disposed at aposition different from that of the vanishing point VP2 of thebackground image 740 d.

More specifically, the vanishing point VP1 of the display object 180 isdisposed higher than the vanishing point VP2 of the background image 740d. In other words, the vanishing point VP1 of the display object 180 isdisposed higher than the vanishing point VP2 of the background image 740d in the case where the human viewer 100 simultaneously views the image181 of the display object 180 and the background image 740 d.

In other words, as viewed by the human viewer 100, the image projectionunit 115 disposes the vanishing point VP1 of the display object 180higher than the vanishing point VP2 of the background image 740 d thatthe human viewer 100 views through the projection plate 715.

Generally, when making images including pictures and the like, avanishing point is used when disposing various objects at depthwardpositions inside the image. For example, the objects are perceived asbeing fixed at the prescribed depthward positions by drawing imaginarystraight lines radially from the prescribed vanishing point and bycausing the outlines and the like of the objects to follow the straightlines. Although vanishing points can be multiply provided, the case isdescribed herein where one vanishing point is provided inside one imageto simplify the description.

Thus, in the formation of a general image, the display object 180 isgenerated such that the position of the vanishing point VP1 of thedisplay object 180 matches the position of the vanishing point VP2 ofthe background image 740 d even in the case of a HUD because the displayobject is generated such that the extension lines of the boundary linesthat form the outlines of the display objects intersect at the vanishingpoint; but in the embodiment, the display object 180 is generated suchthat the position of the vanishing point VP1 of the display object 180is different from the position of the vanishing point VP2 of thebackground image 740 d. The vanishing point VP2 of the background image740 d is inferred from the tilt of the display device 10 and theprojection position 114 a.

Thereby, the depthward set position of the display object 180 can matchthe perceived depthward position of the display object with goodprecision.

The configuration of the embodiment was constructed based on humanperception characteristics that were newly discovered by theexperimental results relating to depth perception described below.

The inventor mounted the display device 10 in the vehicle 730; and aparticipant (the human viewer 100) riding in the passenger seat of thevehicle 730 viewed the images 181 of various display objects 180(arrows) by using the windshield 710 of the vehicle 730 to reflect theimages 181 while the vehicle 730 traveled. Then, an experiment wasperformed by disposing the display object 180 at various depthwardpositions, by changing the size of the display object 180 and the heightfrom the ground surface, and by having the participant respond regardingthe depth distance perceived at that time.

FIG. 6 is a schematic view illustrating the configuration of theevaluation experiment of the characteristics of the display deviceaccording to the first embodiment.

As shown in FIG. 6, the position of the one eye 101 of the participant(the human viewer 100) is taken as the reference point P0; and the depthdirection (the Z-axis direction) distance from the reference point P0 toa set arrangement position Q of the display object 180 is taken as thedepthward set distance Ld. In other words, the set arrangement positionQ is the target position PT of the display object. In this experiment,the three types of depthward set distances Ld of 30 m, 45 m, and 60 mwere used.

The distance between the set arrangement position Q of the displayobject 180 and the ground surface is taken as a set height Δh. In thisexperiment, the three types of set heights Δh of 0 m, 0.5 m, and 1.0 mwere used.

The three types of sizes of the display object 180 when disposed at thepositions corresponding to depthward set distances Ld of 30 m, 45 m, and60 m, respectively, were used. In other words, three types of setdimension distances Sr of 30 m, 45 m, and 60 m corresponding to thesizes of the display objects 180 were used. The set dimension distanceSr is the size of the display object 180 expressed as the depth distanceand is based on the phenomenon of the sense of perspective in whichobjects look smaller as the depthward position increases.

The plane parallel to the ground surface is the X-Z plane. The anglebetween the Z-axis direction and the line connecting the reference pointP0 to the set arrangement position Q of the display object 180 is takenas a depression angle θ. For the depression angle θ, downward (thedirection toward the ground surface) as viewed from the one eye 101 ofthe human viewer 100 is positive.

FIG. 7A to FIG. 7D, FIG. 8A to FIG. 8D, and FIG. 9A to FIG. 9D areschematic views illustrating the conditions of the evaluation experimentof the characteristics of the display device according to the firstembodiment.

Namely, FIGS. 7A to 7D illustrate the change of the depthward setdistance Ld; FIGS. 8A to 8D illustrate the change of the set height Δh;and FIGS. 9A to 9D illustrate the change of the set dimension distanceSr. FIG. 7A, FIG. 8A, and FIG. 9A illustrate the change of the image 181of the display object 180 when changing the depthward set distance Ld,the set height Δh, and the set dimension distance Sr, respectively.FIGS. 7B to 7D, FIGS. 8B to 8D, and FIGS. 9B to 9D illustrate theposition and the size of the image 181 of the display object 180 foreach of the changes.

As shown in FIGS. 7B to 7D, the depthward set distance Ld is changed tobe 30 m, 45 m, and 60 m.

In such a case, as shown in FIG. 7A, the image 181 of the display object180 is changed to be an image D30, an image D45, and an image D60. Inother words, the position of the image 181 moves in the upward Y-axisdirection (the positive direction of the Y-axis) and the size of theimage 181 decreases as the depthward set distance Ld increases.

As illustrated in FIGS. 7B to 7D, the position of the image 181 at thistime changes based on the proportions of the mutual distances of thereference point P0 which is the position of the one eye 101 of the humanviewer 100, the set arrangement position Q of the display object 180,and a projection position P at the reflective surface 712 where thelight flux 112 is projected. In other words, the position of the image181 changes based on the proportion of the triangle having the vertexesof the reference point P0, the set arrangement position Q, and a sethorizontal arrangement position Q1 and the triangle having the vertexesof the reference point P0, the projection position P, and a horizontalprojection position P1. In the specific example, the position of theimage 181 of the display object 180 inside the screen 110 d is caused toshift in the upward direction to correspond to the shift of theprojection position P in the upward direction as the depthward setdistance Ld increases.

As shown in FIGS. 8B to 8D, the set height Δh is changed to be 0 m, 0.5m, and 1.0 m.

In such a case, as shown in FIG. 8A, the image 181 of the display object180 changes to be an image H00, an image H05, and an image H10. In otherwords, the position of the image 181 moves in the upward Y-axisdirection (the positive direction of the Y-axis) as the set height Δhincreases.

In such a case as well, the position of the image 181 changes based onthe proportion of the triangle having the vertexes of the referencepoint P0, the set arrangement position Q, and the set horizontalarrangement position Q1 and the triangle having the vertexes of thereference point P0, the projection position P, and the horizontalprojection position P1 recited above. In the specific example, theposition of the image 181 of the display object 180 inside the image iscaused to shift in the upward direction to correspond to the shift ofthe projection position P in the upward direction as the set height Δhincreases. Because the depression angle θ also changes as the set heightΔh changes, the configuration of the image 181 of the display object 180also changes in conjunction with the change of the depression angle θ.

As shown in FIGS. 9B to 9D, the set dimension distance Sr is changed tobe 30 m, 45 m, and 60 m.

At this time, as shown in FIG. 9A, the image 181 of the display object180 is changed to be an image S30, an image S45, and an image S60. Inother words, the size of the image 181 decreases as the set dimensiondistance Sr increases. This change of the size of the image 181 is basedon the sense of perspective.

The position of the image 181 set based on the proportion of thetriangle having the vertexes of the reference point P0, the setarrangement position Q, and the set horizontal arrangement position Q1and the triangle having the vertexes of the reference point P0, theprojection position P, and the horizontal projection position P1 recitedabove will be called the analogous set position.

FIG. 7A to FIG. 9D recited above are examples in which the depthward setdistance Ld, the set height Δh, and the set dimension distance Sr arechanged independently; but in this experiment, the depth distance (aperceived depth distance Ls) perceived using the display object 180 wasdetermined for a total of 27 types of conditions by using three typesfor each of the depthward set distance Ld, the set height Δh, and theset dimension distance Sr.

FIG. 10A to FIG. 10D, FIG. 11A to FIG. 11D, and FIG. 12A to FIG. 12D aregraphs illustrating the experimental results of the characteristics ofthe display device according to the first embodiment.

Namely, FIGS. 10A to 10D are the results when the depthward set distanceLd was 30 m; FIGS. 11A to 11D are the results when the depthward setdistance Ld was 45 m; and FIGS. 12A to 12D are the results when thedepthward set distance Ld was 60 m.

FIG. 10A, FIG. 11A, and FIG. 12A are the results when the set dimensiondistance Sr was 30 m; FIG. 10B, FIG. 11B, and FIG. 12B are the resultswhen the set dimension distance Sr was 45 m; and FIG. 10C, FIG. 11C, andFIG. 12C are the results when the set dimension distance Sr was 60 m.FIG. 10D, FIG. 11D, and FIG. 12D illustrate the combined results whenthe set dimension distance Sr was 30 m, 45 m, and 60 m.

In these drawings, the horizontal axis is the set height Δh; and thevertical axis is the perceived depth distance Ls. In each of thedrawings, the broken line BL shows the perceived depth distance Ls thatmatches the depthward set distance Ld for that drawing.

FIG. 13A to FIG. 13C are graphs illustrating the experimental results ofthe characteristics of the display device according to the firstembodiment.

Namely, FIGS. 13A to 13C are other graphs illustrating the results ofportions of FIG. 10A to FIG. 12D. These are graphs illustrating theresults of FIG. 10A, FIG. 11B, and FIG. 12C for which the depthward setdistance Ld matches the set dimension distance Sr, where the horizontalaxis is the depthward set distance Ld and the vertical axis is theperceived depth distance Ls. FIGS. 13A to 13C are the results when theset height Δh is 0 m, 0.5 m, and 1.0 m, respectively. In these drawings,the broken line BL shows the case where the depthward set distance Ldmatches the perceived depth distance Ls.

FIG. 10A to FIG. 13C are box plots in which the lower end of the box(the rectangle) is the first quartile; the upper end of the box is thethird quartile; the horizontal line inside the box shows the median; theupper end of the vertical line is the maximum value; the lower end ofthe vertical line is the minimum value; and the “*” marks are outliers.

When the depthward set distance Ld is 30 m as shown in FIGS. 10A to 10D,the perceived depth distance Ls approaches 30 m when the set height Δhis 0 m.

When the depthward set distance Ld is 45 m as shown in FIGS. 11A to 11D,the perceived depth distance Ls approaches 45 m when the set height Δhis 0.5 m.

When the depthward set distance Ld is 60 m as shown in FIGS. 12A to 12D,the perceived depth distance Ls approaches 60 m when the set height Δhis about 1.0 m.

When the depthward set distance Ld is small (e.g., 30 m) as shown inFIGS. 13A to 13C, the depthward set distance Ld and the perceived depthdistance Ls approach each other when the set height Δh is 0 m. As thedepthward set distance Ld increases to 45 m and 60 m, the depthward setdistance Ld and the perceived depth distance Ls approach each other fora larger set height Δh.

Thus, as the depthward set distance Ld increases to 30 m, 45 m, and 60 mand as the set arrangement position Q of the display object 180 becomesdistal to the human viewer 100 as viewed by the human viewer 100, thecorrespondence between the depthward set distance Ld and the perceiveddepth distance Ls increases when the height of the disposition of thedisplay object 180 is shifted upward from the ground surface.

The display object 180 is an arrow; and normally, the display object 180is disposed to match the height of the surface of the road 753 which isthe background image 740 d (i.e., the set height Δh is set to be 0 m).

Thus, when the set height Δh is set to be 0 m, the depthward setdistance Ld and the perceived depth distance Ls are relatively matchedwhen the depthward set distance Ld is 30 m; but the depthward setdistance Ld and the perceived depth distance Ls no longer match as thedepthward set distance Ld exceeds 30 m. It is not conventionally knownthat the set height Δh at which the depthward set distance Ld and theperceived depth distance Ls match thus changes as the depthward setdistance Ld changes in a monocular display. Further, it is notconventionally known that the set height Δh at which the depthward setdistance Ld and the perceived depth distance Ls match increases as thedepthward set distance Ld increases. Such a phenomenon was discoveredfor the first time by this experiment.

This experimental result means that disposing the image 181 of thedisplay object 180 to be shifted higher in the image (in this case,toward the center of the image) than the analogous set position in theimage improves the correspondence between the depthward set distance Ldand the perceived depth distance Ls as the depthward set distance Ldincreases.

Also, considering that the display object 180 is disposed on the road753 side as viewed by the human viewer 100 (the lower side, i.e., thenegative-direction side of the Y-axis) in this experiment, thedisposition of the image 181 of the display object 180 to be shiftedupward in the image corresponds to disposing the image 181 of thedisplay object 180 further from the human viewer 100 as viewed by thehuman viewer 100.

Accordingly, the correspondence between the depthward set distance Ldand the perceived depth distance Ls improves by disposing the image 181of the display object 180 further from the human viewer 100 as viewed bythe human viewer 100 as the depthward set distance Ld increases.

It is conceivable that this phenomenon is a peculiar characteristicrelating to human depth perception when the human views a display withone eye. Because experimental conditions close to actual conditions wereused to display the images 181 of various display objects 180 (arrows)particularly while causing the vehicle 730 to travel in this experiment,a display having a high correspondence between the depthward setdistance Ld and the perceived depth distance Ls can be realizedparticularly for actual conditions such as when traveling, etc., byemploying a configuration in which these results are applied.

In this experiment as illustrated in FIGS. 5A and 5B, the image 181 ofthe display object 180 being disposed further from the human viewer 100as viewed by the human viewer 100 corresponds to the display object 180being disposed higher because the display object 180 is disposed lowerthan the human viewer 100 as viewed by the human viewer 100.

On the other hand, as illustrated in FIGS. 5C and 5D, in the case wherethe display object 180 is disposed higher than the human viewer 100 asviewed by the human viewer 100, disposing the image 181 of the displayobject 180 further from the human viewer 100 as viewed by the humanviewer 100 corresponds to disposing the display object 180 lower.

In other words, in the case where the depthward set distance Ld islarge, the image 181 of the display object 180 may be disposed to bemore distal than is the position that is based on the analogous setposition. In the case where the display object 180 is disposed lowerthan the human viewer 100 as viewed by the human viewer 100, the displayobject 180 is disposed higher than the position that is based on theanalogous set position. In the case where the display object 180 isdisposed higher than the human viewer 100 as viewed by the human viewer100, the display object 180 is disposed lower than the position that isbased on the analogous set position.

Then, based on such new knowledge relating to this peculiarcharacteristic relating to human depth perception, in the display device10 according to the embodiment, the vanishing point VP1 of the displayobject 180 is disposed to be more distal to the human viewer 100 asviewed by the human viewer 100 than is the vanishing point VP2 of thebackground image 740 d that the human viewer 100 views through theprojection plate 715.

In other words, the vanishing point VP1 of the display object 180 isdisposed at a position different from that of the vanishing point VP2 ofthe background image 740 d.

For example, the vanishing point VP1 of the display object 180 isdisposed higher than the vanishing point VP2 of the background image 740d in the case where the display object 180 is disposed lower than thehuman viewer 100 as viewed by the human viewer 100.

For example, the vanishing point VP1 of the display object 180 isdisposed lower than the vanishing point VP2 of the background image 740d in the case where the display object 180 is disposed higher than thehuman viewer 100 as viewed by the human viewer 100.

Thereby, the perception of the depthward position of the display object180 can be provided to match the position of the background image 740 dwith good precision by conforming to human depth perception. Then, thedisplay object 180 can be perceived to be at the desired depthwardposition by reducing the fluctuation due to the human viewer of theperceived depthward position.

The control of the vanishing point VP1 of the display object 180 willnow be described in more detail.

FIG. 14A to FIG. 14D are schematic views illustrating operations of thedisplay device according to the first embodiment.

Namely, FIGS. 14A and 14B correspond to the case where the displayobject 180 is disposed lower than the human viewer 100 as viewed by thehuman viewer 100. On the other hand, FIGS. 14C and 14D correspond to thecase where the display object 180 is disposed higher than the humanviewer 100 as viewed by the human viewer 100.

FIGS. 14A and 14C show states in which the depthward position indicatedby the display object 180 is disposed to be more distal than is thebackground image 740 d. FIGS. 14B and 14D show states in which theposition indicated by the display object 180 is disposed at the samedepthward position as the background image 740 d. In these drawings,model-like illustrations of the boundaries 753 a and 753 b on two sidesof the road 753 are provided as the background image 740 d.

First, the case where the display object 180 is disposed lower than thehuman viewer 100 as viewed by the human viewer 100 will be described.

As shown in FIG. 14A, the vanishing point VP1 of the display object 180is disposed higher than the vanishing point VP2 of the background image740 d as viewed by the human viewer 100. Thereby, the depthward positionindicated by the display object 180 is disposed to be more distal thanis the background image 740 d. By using such a display object 180, forexample, the perceived depth distance Ls and the depthward set distanceLd that are perceived by the human viewer 100 become well-matched in thecase where the set arrangement position Q is relatively distal when thedepthward set distance Ld is 45 m to 60 m as illustrated in FIG. 11A toFIG. 12D.

As shown in FIG. 14B, the vanishing point VP1 of the display object 180matches the vanishing point VP2 of the background image 740 d. In thiscase, the depthward position indicated by the display object 180 matchesthe depthward position of the background image 740 d. By using such adisplay object 180, the perceived depth distance Ls and the depthwardset distance Ld that are perceived by the human viewer 100 arewell-matched in the case where, for example, the set arrangementposition Q is relatively proximal when the depthward set distance Ld is30 m as illustrated in FIGS. 10A to 10D.

The case where the display object 180 is disposed higher than the humanviewer 100 as viewed by the human viewer 100 will now be described.

As shown in FIG. 14C, the vanishing point VP1 of the display object 180is disposed lower than the vanishing point VP2 of the background image740 d as viewed by the human viewer 100. Thereby, the depthward positionindicated by the display object 180 is disposed to be more distal thanis the background image 740 d. By using such a display object 180, theperceived depth distance Ls and the depthward set distance Ld that areperceived by the human viewer 100 become well-matched in the case where,for example, the set arrangement position Q is relatively distal whenthe depthward set distance Ld is 45 m to 60 m as illustrated in FIG. 11Ato FIG. 12D.

As shown in FIG. 14D, the vanishing point VP1 of the display object 180matches the vanishing point VP2 of the background image 740 d. In thiscase, the depthward position indicated by the display object 180 matchesthe depthward position of the background image 740 d. By using such adisplay object 180, the perceived depth distance Ls and the depthwardset distance Ld that are perceived by the human viewer 100 arewell-matched in the case where, for example, the set arrangementposition Q is relatively proximal when the depthward set distance Ld is30 m as illustrated in FIGS. 10A to 10D.

Thus, the image projection unit 115 disposes the display object 180lower than the human viewer 100 as viewed by the human viewer 100 anddisposes the vanishing point VP1 of the display object 180 higher asviewed by the human viewer 100 than the vanishing point VP2 of thebackground image 740 d viewed by the human viewer 100 through theprojection plate. Or, the image projection unit 115 disposes the displayobject 180 higher than the human viewer 100 as viewed by the humanviewer 100 and disposes the vanishing point VP1 of the display object180 lower than the vanishing point VP2 of the background image 740 d asviewed by the human viewer 100.

More specifically, the image projection unit 115 causes the differencebetween the vanishing point VP1 of the display object 180 and thevanishing point VP2 of the background image 740 d to change based on thetarget position PT at which the display object 180 is disposed (theposition at the depthward set distance Ld as viewed by the human viewer100).

In other words, for example, the position of the vanishing point VP1 ofthe display object 180 is caused to match the position of the vanishingpoint VP2 of the background image 740 d by, for example, reducing thedifference between the vanishing point VP1 of the display object 180 andthe vanishing point VP2 of the background image 740 d when the depthwardset distance Ld is not more than about 30 m.

Then, for example, the position of the vanishing point VP1 of thedisplay object 180 is caused to be different from the position of thevanishing point VP2 of the background image 740 d by increasing thedifference between the vanishing point VP1 of the display object 180 andthe vanishing point VP2 of the background image 740 d when the depthwardset distance Ld is greater than about 30 m, e.g., not less than 45 m.

Thereby, the depthward set position of the display object can match theperceived depthward position of the display object with good precisionby corresponding to human depth perception characteristics when thedepthward set distance Ld is changed as described in regard to FIG. 10Ato FIG. 13C.

In other words, the display object 180 can be perceived with goodprecision at the desired depthward position by reducing individualdifferences of the perceived depthward positions when the display object180 is viewed; and it is possible to realize a high-precision depthwarddisposition using a background superimposition-type monocular display.

As recited above, it is desirable for the difference between thevanishing point VP1 of the display object 180 and the vanishing pointVP2 of the background image 740 d to be greater when the depthward setdistance Ld is large than when the depthward set distance Ld is small.Thereby, the precision of the perceived depthward position is evenhigher.

FIG. 15A and FIG. 15B are schematic views illustrating operations of thedisplay device according to the first embodiment.

Namely, these drawings illustrate the display object 180 in the casewhere an arrow that provides a prompt to change the route to the rightis used as the display object 180. In other words, the road 753 of thebackground image 740 d has a branch road that branches to the right.FIG. 15A is an example in which the vanishing point VP1 of the displayobject 180 is disposed higher than the vanishing point VP2 of thebackground image 740 d; and FIG. 15B is an example in which thevanishing point VP1 of the display object 180 matches the vanishingpoint VP2 of the background image 740 d.

As shown in FIG. 15A, the angle between the two sides 183 a and 183 b ofthe shaft portion of the arrow of the display object 180 is relativelysmall. Thereby, the vanishing point VP1 of the display object 180 isdisposed higher than the vanishing point VP2 of the background image 740d.

As shown in FIG. 15B, the angle between the sides 183 a and 183 b of thearrow of the display object 180 is relatively large. Thereby, thevanishing point VP1 of the display object 180 matches the vanishingpoint VP2 of the background image 740 d.

In both FIGS. 15A and 15B, the tip of the arrow of the display object180 is disposed in the direction of the branch road 753; and the arrowis bent to indicate the direction to change the route.

Thus, the vanishing point VP1 of the display object 180 can be changedby changing the angles of the sides 183 a and 183 b of the displayobject 180, i.e., the angles of the outlines of the display object 180.

The depthward set position of the display object can match the perceiveddepthward position of the display object with good precision by, forexample, employing the configuration of the display object 180illustrated in FIG. 15B when the depthward set distance Ld is not morethan about 30 m and by, for example, employing the configuration of thedisplay object 180 illustrated in FIG. 15A when the depthward setdistance Ld is greater than about 30 m, e.g., 45 m or greater.

An example of a method for defining the target position PT of thedisplay object 180 will now be described.

FIG. 16 is a schematic view illustrating the configuration of anotherdisplay device according to the first embodiment.

As shown in FIG. 16, the display device 11 a according to the embodimentfurther includes an external environment information acquisition unit410 that acquires the external environment information of the vehicle730 in which the image projection unit 115 is mounted.

The image projection unit 115 projects the light flux 112 by adjustingthe vanishing point VP1 of the display object 180 to correspond to thetarget position PT of the display object 180 based on the externalenvironment information acquired by the external environment informationacquisition unit 410.

In other words, for example, the image data generation unit 130 of theimage projection unit 115 generates the data relating to the imageincluding the display object 180 based on the external environmentinformation acquired by the external environment information acquisitionunit 410; the image is formed by the image formation unit 110; and thelight flux 112 is projected by the projection unit 120.

The external environment information acquisition unit 410 acquires, forexample, the travel direction of the road, the width of the road, theconfiguration of the road, the existence of branch points, theconfigurations of branch points, etc., as the external environmentinformation of the vehicle 730. Any method can be employed as thisacquisition method, including methods that use a storage unit in whichsuch external information is stored beforehand, various methods toacquire the external information by wireless communication asappropriate, etc. Examples of acquisition methods of the externalinformation are described below.

FIG. 17 is a flowchart illustrating operations of another display deviceaccording to the first embodiment.

First, as shown in FIG. 17, for example, the route in which it ispresumed that the vehicle 730 in which the display device 11 a ismounted will travel is generated (step S110). For example, the route isgenerated based on the prescribed map information and the like by usingthe relationship between the current position of the vehicle 730 and thedestination of the vehicle 730 determined by a GPS (Global PositioningSystem) function and the like. The generation of this route may beperformed inside the display device 10 and by a navigation system andthe like mounted in the vehicle; and this route may be generated usingany method.

Then, the external environment information is acquired by the externalenvironment information acquisition unit 410 (step S120). For example,information such as the state of the frontward road of the vehicle 730,the existence of branch points, etc., are acquired as the externalenvironment information at the current position of the vehicle 730 fromthe relationship between the generated route and the current position ofthe vehicle 730 determined by a GPS function and the like.

Continuing, the external environment display position where the displayobject 180 is to be displayed such as the position of a branch pointwhere the route is to be changed is derived (step S130).

Then, the target position PT of the display object 180 is derived basedon the derived external environment display position (step S140). Forexample, the target position PT is determined based on the derivedexternal environment display position (e.g., the position of the branchpoint) and the current position of the vehicle 730.

Continuing, the image data including the display object 180 is generatedbased on the target position PT (step S150). For example, the size, theconfiguration, and the position of the display object 180 inside thescreen 110 d are determined based on the target position PT and theposition of the one eye 101 of the human viewer 100; and data of thedisplay object 180 that has such a position, size, and configuration isgenerated.

At this time, the vanishing point VP1 of the display object 180 isadjusted in the display device 11 a according to the embodiment. Inother words, the positions of the vanishing point VP1 of the displayobject 180 and the vanishing point VP2 of the background image 740 d arecaused to be different or to match according to, for example, thedepthward set distance Ld which is the distance to the target positionPT of the display object 180. Whether to dispose the vanishing point VP1of the display object 180 higher than or lower than the vanishing pointVP2 of the background image 740 d is changed according to whether thedisplay object 180 is disposed lower than or higher than the humanviewer 100 as viewed by the human viewer 100.

Then, the distortion of the image including the display object 180 isappropriately corrected (step S160); and the image data is outputted(step S170).

Step S130 to step S160 recited above may be executed in, for example,the image data generation unit 130. However, a portion of step S130 tostep S170 may be executed in, for example, the external environmentinformation acquisition unit 410 and other units.

Then, the image is formed by the image formation unit 110 based on theimage data; and the light flux 112 including the image is projectedtoward the human viewer 100 by the projection unit 120 (step S180).

In step S150 recited above, the method for generating the data of thedisplay object 180 by adjusting the position of the vanishing point VP1of the display object 180 is arbitrary. For example, the image data inwhich the vanishing point VP1 is controlled is made at the initial stagein which the display object 180 is generated. The modifications relatingto the size, the angle, the arrangement position, and the like areperformed based on the image data. The modified image may be used as theimage data of the final display object 180. Also, a modification of theimage to change the vanishing point VP1 may be performed afterperforming the modification relating to the size, the angle, thearrangement position, and the like of the display object 180. In otherwords, when performing the shift of the vanishing point VP1 of thedisplay object 180, a method can be employed in which the image data isgenerated after the shift value is provided. A method also can beemployed in which the image data is modified further using the shiftvalue after the image data is generated. A unit for performing such acalculation may be further provided separately from the image projectionunit 115; and, for example, the image data generation unit 130 may beused to implement such a calculation inside the image projection unit115.

Thus, the target position PT of the display object 180 can beefficiently derived and the control relating to the vanishing point VP1of the display object 180 can be efficiently implemented by furtherincluding the external environment information acquisition unit 410.

The external environment information acquisition unit having thefunctions recited above may be provided outside the display deviceaccording to the embodiment; and the operations described above can beimplemented by acquiring the necessary data from the externalinformation acquisition unit provided externally.

FIG. 18 is a schematic view illustrating the configuration of anotherdisplay device according to the first embodiment.

As shown in FIG. 18, the display device 11 b further includes a routegeneration unit 450 that generates the route in which it is presumedthat the vehicle 730 will travel. Otherwise, the display device 11 b maybe similar to the display device 11 a, and a description is omitted.

The route generation unit 450 calculates the route in which it ispresumed that the vehicle 730 will travel based on the externalenvironment information acquired by the external environment informationacquisition unit 410 and, for example, the current position of thevehicle 730. At this time, for example, several route alternatives maybe calculated; the human viewer 100 who is the operator of the vehicle730 may be prompted for a selection; and the route may be determinedbased on the results.

Thus, the route can be generated efficiently inside the display device11 b by further providing the route generation unit 450.

FIG. 19 is a schematic view illustrating the configuration of anotherdisplay device according to the first embodiment.

As shown in FIG. 19, the display device 11 c includes an externalenvironment information data storage unit 410 a in which the externalenvironment information of the vehicle 730 is stored beforehand.Thereby, the external environment information acquisition unit 410acquires data relating to the external environment information storedbeforehand in the external environment information data storage unit 410a.

The external environment information data storage unit 410 a may includea magnetic recording and reproducing device such as a HDD, etc., arecording device based on an optical method such as a CD, DVD, etc., andvarious storage devices using semiconductors.

Various information relating to the configurations of roads and branchpoints, place names, buildings, target objects, etc., outside thevehicle 730 may be stored as the external environment information of thevehicle 730 in the external environment information data storage unit410 a. Thereby, the external environment information acquisition unit410 can read the external environment information from the externalenvironment information data storage unit 410 a based on the currentposition of the vehicle 730 and supply the external environmentinformation to the image data generation unit 130.

When reading the information stored in the external environmentinformation data storage unit 410 a, the current position of the vehicle730 (the human viewer 100) can be ascertained and the travel directioncan be ascertained using, for example, GPS and the like; and theexternal environment information corresponding to the position and thetravel direction can be read based on the position and the traveldirection.

FIG. 20 is a schematic view illustrating the configuration of anotherdisplay device according to the first embodiment.

As shown in FIG. 20, the external environment information acquisitionunit 410 of the display device 11 d includes an external environmentinformation detection unit 420 configured to detect the frontwardexternal environment information of the vehicle 730.

In the specific example, the external environment information detectionunit 420 includes an external environment imaging unit 421 (a camera),an image analysis unit 422 configured to perform image analysis of theimage that is captured by the external environment imaging unit 421, andan external environment information generation unit 423 that extractsvarious information relating to the configurations of roads and branchpoints, obstacles, etc., from the image analyzed by the image analysisunit 422 to generate the external environment information. Thereby, datarelating to the road conditions of the external environment (theconfigurations of roads and branch points, obstacles, etc.) detected bythe external environment information detection unit 420 are acquired.The external environment information detection unit 420 may be designedto generate the external environment information by reading a signalfrom various guidance signal emitters such as beacons and the likeprovided on the road on which the vehicle 730 travels.

Thus, the external environment information detection unit 420 that isconfigured to detect the frontward external environment information ofthe vehicle 730 is provided in the display device 11 d according to theexample. The external environment information acquisition unit 410 canacquire the frontward external environment information of the vehicle730 that changes moment to moment. Thereby, the external environmentinformation that changes moment to moment can be acquired; and thetravel direction of the vehicle 730 can be calculated with betterprecision.

FIG. 21 is a schematic view illustrating the configuration of anotherdisplay device according to the first embodiment.

As shown in FIG. 21, a vehicle position detection unit 430 that isconfigured to detect the position of the vehicle 730 is further providedin the display device 11 e. The vehicle position detection unit 430 mayuse, for example, GPS. The display object 180 is generated based on theposition of the vehicle 730 detected by the vehicle position detectionunit 430.

In other words, the display object 180 is disposed based on the externalenvironment information from the external environment informationacquisition unit 410 and the position of the vehicle 730 detected by thevehicle position detection unit 430. Thereby, the display object 180 canbe displayed based on the precise position of the vehicle 730.

At least one selected from the route generation unit 450, the externalenvironment information data storage unit 410 a, the externalenvironment information detection unit 420, and the vehicle positiondetection unit 430 described above may be built into the imageprojection unit 115 of the display device.

At least one selected from the route generation unit 450, the externalenvironment information data storage unit 410 a, the externalenvironment information detection unit 420, and the vehicle positiondetection unit 430 may be provided outside the display device accordingto the embodiment and may be provided outside the vehicle 730 in whichthe display device is mounted. In such a case, the operations recitedabove are performed by performing input/output of the data from unitscorresponding to the route generation unit, the external environmentinformation data storage unit, the external environment informationdetection unit, and the vehicle position detection unit provided outsidethe vehicle 730 by using, for example, wireless technology and the like.

FIG. 22 is a schematic view illustrating the configuration of anotherdisplay device according to the first embodiment.

In the display device 12 as shown in FIG. 22, the external environmentinformation acquisition unit 410, a position detection unit 210, and acontrol unit 250 are further provided in the display device 10illustrated in FIG. 2. The external environment information acquisitionunit 410 may be similar to that recited above, and a description isomitted.

The position detection unit 210 is configured to detect the one eye 101of the human viewer 100. The position detection unit 210 may include,for example, an imaging unit 211 configured to capture an image of thehuman viewer 100, an image processing unit 212 configured to performimage processing of the image captured by the imaging unit 211, and acalculation unit 213 configured to determine and detect the position ofthe one eye 101 of the human viewer 100 based on the data from the imageprocessing of the image processing unit 212.

The calculation unit 213 determines and detects the position of the oneeye 101 of the human viewer 100 onto which the image is to be projectedby using face recognition of the human viewer 100 and calculating theeyeball positions as facial parts using any technology relating topersonal authentication.

The imaging unit 211 is disposed, for example, frontward and/or sidewardof the driver's seat of the vehicle 730 to capture, for example, animage of the face of the human viewer 100, i.e., the operator; and theposition of the one eye 101 of the human viewer is detected as recitedabove.

The control unit 250 adjusts at least one selected from the projectionarea 114 and the projection position 114 a of the light flux 112 bycontrolling the image projection unit 115 based on the position of theone eye 101 of the human viewer 100 detected by the position detectionunit 210.

The control unit 250 controls, for example, the projection position 114a by controlling the angle of the mirror 126 by controlling a drive unit126 a linked to the mirror 126 which is a portion of the projection unit120.

The control unit 250 can control the projection area 114 by controlling,for example, various optical parts included in the projection unit 120.

Thereby, it is possible to control the presentation position of theimage to follow the head 105 of the human viewer 100 even in the casewhere the head 105 of the human viewer 100 moves. The image presentationposition moving out of the position of the one eye 101 due to themovement of the head 105 of the human viewer 100 is suppressed; and awider practical viewing area is possible.

The control unit 250 may adjust the luminance, the contrast, and thelike of the image by, for example, controlling the image formation unit110. Although the at least one selected from the projection area 114 andthe projection position 114 a of the light flux 112 is adjustedautomatically by the control unit 250 based on the position of thedetected one eye 101 in the specific example recited above, theembodiments are not limited thereto. For example, the at least oneselected from the projection area 114 and the projection position 114 aof the light flux 112 may be adjusted manually based on the position ofthe detected one eye 101. In such a case, the angle of the mirror 126can be controlled by, for example, manually controlling the drive unit126 a while viewing the image of the head 105 of the human viewer 100captured by the projection unit 120 on some kind of display.

In the display device 12 of the specific example, a combiner 711 (areflective layer) is provided in the windshield 710. The combiner 711may be used as the projection plate 715. The transmittance of the lightof the background image 740 d and/or the reflectance of the light flux112 can be increased further by appropriately designing the opticalcharacteristics of the combiner 711; and a display that is even easierto view can be realized.

At least two selected from the route generation unit 450, the externalenvironment information data storage unit 410 a, the externalenvironment information detection unit 420, the vehicle positiondetection unit 430, the position detection unit 210, and the controlunit 250 described above may be provided simultaneously.

Second Embodiment

FIG. 23 is a flowchart illustrating the display method according to asecond embodiment.

As shown in FIG. 23, the display method according to the embodimentprojects the light flux 112 that includes the image including thedisplay object 180 toward the one eye 101 of the human viewer 100 byusing the reflective and transmissive projection plate 715 to reflectthe light flux 112. The vanishing point VP1 of the display object 180 isdisposed at a position different from that of the vanishing point VP2 ofthe background image 740 d viewed by the human viewer 100 through theprojection plate 715 (step S10).

Then, the light flux 112 that includes the image including the displayobject 180 is projected toward the one eye 101 of the human viewer 100by using the projection plate 715 to reflect the light flux 112 (stepS20).

For example, the vanishing point VP1 of the display object 180 isdisposed higher than the vanishing point VP2 of the background image 740d in the case where the display object 180 is disposed lower than thehuman viewer 100 as viewed by the human viewer 100.

Then, for example, the vanishing point VP1 of the display object 180 isdisposed lower than the vanishing point VP2 of the background image 740d in the case where the display object 180 is disposed higher than thehuman viewer 100 as viewed by the human viewer 100.

Thereby, the depthward set position of the display object can match theperceived depthward position of the display object with good precisionby conforming to human depth perception.

According to the embodiments, a monocular display device and displaymethod are provided in which the depthward set position of the displayobject and the perceived depthward position of the display object arematched with good precision.

Hereinabove, exemplary embodiments of the invention are described withreference to specific examples. However, the invention is not limited tothese specific examples. For example, one skilled in the art maysimilarly practice the invention by appropriately selecting specificconfigurations of components such as image projection units, image datageneration units, image formation units, projection units, lightsources, diffuser plates, tapered light guides, lenses, apertures,mirrors, route generation units, external environment information datastorage units, external environment information detection units, vehicleposition detection units, position detection units, control units, etc.,included in display devices from known art; and such practice isincluded in the scope of the invention to the extent that similareffects are obtained.

Further, any two or more components of the specific examples may becombined within the extent of technical feasibility and are included inthe scope of the invention to the extent that the purport of theinvention is included.

Moreover, all display devices practicable by an appropriate designmodification by one skilled in the art based on the display devicesdescribed above as embodiments of the invention also are within thescope of the invention to the extent that the spirit of the invention isincluded.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the invention.

What is claimed is:
 1. A display device, comprising: an image projectionunit configured to project a light flux toward one eye of a human viewerby using a projection plate to reflect the light flux, the light fluxincluding an image including a display object having a vanishing point,the projection plate being reflective and transmissive, the imageprojection unit being configured to dispose the vanishing point of thedisplay object at a position different from a position of a vanishingpoint of a background image viewed by the human viewer through theprojection plate, wherein the image projection unit disposes the displayobject at a position lower than a position of a center of a reflectivesurface of the projection plate as viewed by the human viewer anddisposes the vanishing point of the display object at a position higherthan a position of the vanishing point of the background image as viewedby the human viewer.
 2. The device according to claim 1, wherein theimage projection unit includes a first lens, a second lens, and adivergence angle control element provided between the first lens and thesecond lens, the divergence angle control element being configured tocontrol a divergence angle of the light flux.
 3. The device according toclaim 2, wherein the divergence angle control element is an aperturehaving an opening having a variable size.
 4. The device according toclaim 2, wherein the first lens has a first focal distance; the secondlens has a second focal distance; a distance between the divergenceangle control element and the first lens is the first focal distance;and a distance between the divergence angle control element and thesecond lens is the second focal distance.
 5. The device according toclaim 1, wherein the display object has a configuration including afirst side and a second side; and an extension line of the first sideintersects an extension line of the second side at the vanishing pointof the display object.
 6. The device according to claim 1, wherein aprojection area of the light flux at a position of the human viewer hasa lateral-direction width not more than 70 millimeters as viewed by thehuman viewer.
 7. The device according to claim 1, wherein the imageprojection unit changes a difference between the vanishing point of thedisplay object and the vanishing point of the background image based ona target position of the display object.
 8. The device according toclaim 7, wherein the image projection unit causes the position of thevanishing point of the display object to match the position of thevanishing point of the background image when a depthward set distancebetween the target position and a position of the one eye is not morethan 30 meters, and the image projection unit causes the position of thevanishing point of the display object to be different from the positionof the vanishing point of the background image when the depthward setdistance is greater than 30 meters.
 9. The device according to claim 8,wherein the image projection unit causes the position of the vanishingpoint of the display object to be different from the position of thevanishing point of the background image when the depthward set distanceis not less than 45 meters.
 10. The device according to claim 1, whereinthe display device is mounted in a vehicle; and the projection plate isa windshield unit of the vehicle.
 11. A display device, comprising: animage projection unit configured to project a light flux toward one eyeof a human viewer by using a projection plate to reflect the light flux,the light flux including an image including a display object having avanishing point, the projection plate being reflective and transmissive,the image projection unit being configured to dispose the vanishingpoint of the display object at a position different from a position of avanishing point of a background image viewed by the human viewer throughthe projection plate, wherein the image projection unit disposes thedisplay object at a position higher than a position of a center of areflective surface of the projection plate as viewed by the human viewerand disposes the vanishing point of the display object at a positionlower than a position of the vanishing point of the background image asviewed by the human viewer.
 12. A display method, comprising: projectinga light flux including an image including a display object toward oneeye of a human viewer by using a projection plate to reflect the lightflux, the projection plate being reflective and transmissive; disposinga vanishing point of the display object at a position different from aposition of a vanishing point of a background image viewed by the humanviewer through the projection plate during the projecting toward the oneeye; disposing the display object at a position lower than a position ofa center of a reflective surface of the projection plate as viewed bythe human viewer; and disposing the vanishing point of the displayobject at a position higher than a position of the vanishing point ofthe background image as viewed by the human viewer.
 13. The methodaccording to claim 12, wherein the projecting toward the one eyeincludes projecting the light flux toward the one eye by using theprojection plate to reflect the light flux by using a first lens, asecond lens, and a divergence angle control element provided between thefirst lens and the second lens, the divergence angle control elementbeing configured to control a divergence angle of the light flux. 14.The method according to claim 13, further comprising: changing adifference between the vanishing point of the display object and thevanishing point of the background image based on a target position ofthe display object.
 15. The method according to claim 14, wherein theimage projection unit causes the position of the vanishing point of thedisplay object to match the position of the vanishing point of thebackground image when a depthward set distance between the targetposition and a position of the one eye is not more than 30 meters; andthe image projection unit causes the position of the vanishing point ofthe display object to be different from the position of the vanishingpoint of the background image when the depthward set distance is greaterthan 30 meters.
 16. The method according to claim 15, wherein the imageprojection unit causes the position of the vanishing point of thedisplay object to be different from the position of the vanishing pointof the background image when the depthward set distance is not less than45 meters.
 17. The method according to claim 12, wherein the projectionplate is a windshield unit of the vehicle.
 18. A display method,comprising: projecting a light flux including an image including adisplay object toward one eye of a human viewer by using a projectionplate to reflect the light flux, the projection plate being reflectiveand transmissive; disposing a vanishing point of the display object at aposition different from a position of a vanishing point of a backgroundimage viewed by the human viewer through the projection plate during theprojecting toward the one eye; disposing the display object at aposition higher than a position of a center of a reflective surface ofthe reflection plate as viewed by the human viewer; and disposing thevanishing point of the display object at a position lower than aposition of the vanishing point of the background image as viewed by thehuman viewer.